Roadside signs have long been effective means for advertising and conveying messages. Known billboard style signs are advantageous in that they successfully advertise a message to a broad audience for a relatively low price. However, these signs suffer from a severe disadvantage in that their display message may be posted for weeks or months limiting their effectiveness over the long term. The viewing audience simply becomes bored with the same inanimate sign displaying the same message, and its marketing effectiveness drops off significantly over time.
In response to conventional forms of billboard advertising, multi-sided, segmented, rotating signs were developed. These signs typically comprise a number of three-sided sign segments driven by a motor that selectively starts and stops or by a motor having some type of trip mechanism or clutch. One example of this type of sign is disclosed in U.S. Pat. No. 3,387,394.
Multi-sided, segmented, rotating signs are typically designed such that all of the segments rotate together and are not designed to allow one segment to remain stationary for an extended period. However, because these signs are often installed outside and exposed to the elements, one or more segments of the rotating sign may become jammed. This could occur due to dirt or debris becoming lodged around one of the segments or due to failure of the bearings that support the sign segment. To address this problem, currently existing rotating signs may include some type of "weak link" which is designed to fail if a sign segment becomes jammed. This "weak link" may be provided by constructing one of the drive gears from a softer material so that the gear fails in the event a segment becomes jammed. It is also possible to design the interconnection between a shaft and a gear to perform as a weak link or to form some portion of the drive mechanism, such as an interconnecting shaft, of a weak material so that it is the first to fail. Disadvantages to this approach are that a "weak link" is only capable of one failure and therefore is not resettable. Once the "weak link" fails, it is necessary to disassemble a portion of the sign and replace the part which has failed. A second disadvantage is that a "weak link" is typically not adjustable. It will always fail at approximately the same level of force independent of the application of the sign. To change the level of force required to make the "weak link" fail requires redesigning the "weak link" for the new application. Rotating signs come in a variety of sizes and are installed in a variety of conditions, and therefore the desirable force at which a weak link should fail may vary.
A second approach to allowing one sign segment to cease rotation is to limit the output of the drive motor. For example, it would be possible to use a drive motor with limited output torque and to wire the motor with a circuit breaker or fuse which will fail if the motor is unable to continue rotating the sign segments if it begins to overload or overheat. Like the "weak link," this approach suffers from a lack of resettability as well as limited adjustability. Unlike the "weak link" this approach stops all of the segments. Also, limiting the torque output of a drive motor may be undesirable as the total torque required to rotate the sign segments may vary dramatically depending upon weather conditions as well as the amount of wear in the total system. Therefore it makes it very difficult to predict what level of torque output is desirable. Therefore, there is a need for a device which allows one or more segments of a rotatable sign assembly to cease rotating and also provides for resettability and/or adjustability.